Containers such as buckets and pails of unitary construction molded from plastic materials have become more widespread in use during recent years, due in part to the fact that they may be economically produced in large quantities. Molded plastic containers have replaced many types of previous metal constructions except in those applications where hazardous materials such as paints and thinners are intended to be packaged; these latter mentioned applications demand that the container be exceptionally rigid and not subject to rupture or leakage during shipping or ordinary use. Molded plastic containers have not been entirely successful in replacing metal constructions because prior art container-to-lid interlocks have not been entirely reliable in providing a seal which precludes leakage of the contents from the container. Although interlocks, such as that disclosed in U.S. Pat. No. 3,977,563, have previously been designed which form an essentially fluid tight seal under ordinary conditions of use, such seal may be easily broken and the lid inadvertently removed from the container if the rim is flexed.
Containers, such as those used to package paint and the like, are desirably formed with essentially smooth sidewalls, free of protuberances, so that the containers may be placed in side-by-side relationship to each other in a minimum amount of space. Reinforcement ribs, as shown in the disclosure of U.S. Pat. No. 3,977,563, extend radially outward beyond the sidewalls of the container and therefore increased the amount of space needed to package a number of such containers for shipping and storage purposes.
Another disadvantage of prior art containers of the type mentioned above resides in the fact that such containers possess relatively little axial strength adjacent the rim thereof, compared to metal constructions. Weakness in the rim in the axial direction results in the rim flexing or bowing, or otherwise deforming when a lid is either pried from, or applied to, the container under pressure.
Accordingly, it is an important object of the present invention to provide a molded plastic container assembly having an improved rim-to-lid interlock which provides a positive, reliable fluid tight seal even when subjected to rough handling, as during shipping thereof.
A further important object of the invention is to provide a container assembly of the type mentioned above which exhibits improved rigidity in the axial direction adjacent the rim, so as to preclude flexing of the rim during installation or removal of a lid from the container.
A still further object of the invention is to provide a container assembly as described above which is provided with longitudinal and circumferential reinforcement ribs adjacent the rim of the container which are inset into the container sidewalls, such that such sidewalls exhibit an essentially smooth, uninterrupted profile.
These and further objects of the invention will be made clear or will become apparent during the course of the following description of a preferred embodiment of the invention.